It is standard to close a bottle (which term is here intended to cover any recipient intended to hold a fluent material and having a rigid tubular mouth through which the contents pass) by providing its mouth with external threads that can mate with internal threads of a normally cup-shaped cap. The bottle, which is typically made of glass or plastic, can also be formed on its neck with a retaining ridge under which engage elements of an antitamper ring that is secured by frangible webs to the body of the cap. Thus if the cap is removed, these webs will be ruptured to give a clear indication to the consumer that the container has been tampered with.
In order to seal as well as possible it is known to provide the body part of the cap with a seal ring that engages inside the mouth of the bottle neck. Such caps work just fine so long as they are accurately dimensioned with respect to the bottle they are used on. If the tolerances vary somewhat, however, the lip will not seat properly and the cap will leak. Such variations in tolerance can occur depending, for example, on whether the bottle is made of disposable or recyclable PET, or of PVC or glass. Thus the caps must be exactly manufactured depending on the construction and material of the bottle they are to be used on. Any minor variation from tolerances will result in a leak.
It is also possible to provide a nonintegral seal ring as a separate piece in the cap. This construction is more tolerant of a bad fit, but costs considerably more to make and is much harder to recycle.
In another system a one-piece cap has a seal lip that engages axially against the end surface of the bottle mouth. While such a cap is more tolerant of a bad fit, it cannot hold against much pressure. Thus it is not suitable for use, for instance, on a bottle holding a carbonated beverage where internal pressure can be several bar. Furthermore such a lip is frequently fairly fragile so that it can tear or wrinkle during mounting of the cap, producing a site for a leak.
German utility model 9,208,944 describes a cap having an end wall and a skirt projecting axially downward therefrom. The skirt is internally threaded to fit with the external screwthread of the bottle neck and the end wall has a seal ring that ends at an expansion. When this cap is screwed onto a bottle the ring stretches without movement into the bottle mouth which is thus pressed against this ring and the skirt. This cap is fairly good, but is, once again, very sensitive to dimensions in that it must be exactly fitted to the bottle it is used on.
As far as the antitamper ring is concerned, these are frequently left on the bottle in the prior art. When the cap is made of a resin different from that of the bottle, this creates a recycling problem as the ring must be cut off the bottle before it can be recycled. Furthermore it is occasionally possible to remove such a cap without separating it from its antitamper ring, and such caps can often not be installed by fast-acting machinery without damage to the antitamper structure.